Telecommunications systems and methods for machine type communication

ABSTRACT

A method for communicating data between a base station and a terminal device in a wireless telecommunications system, for example an LTE-based system. The wireless communication system uses plural frequency sub-carriers spanning a system frequency band. Physical-layer control information for the terminal device is transmitted from the base station using sub-carriers selected from across the system frequency band, for example to provide frequency diversity. However, higher-layer data for the terminal device is transmitted using only sub-carriers selected from within a restricted frequency band which is smaller than and within the system frequency band. The terminal device is aware of the restricted frequency band, and as such need only buffer and process data within this restricted frequency band during periods where higher-layer data is being transmitted. The terminal device buffers and processes the full system frequency band during periods when physical-layer control information is transmitted.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application which claims thebenefit of priority under 35 U.S.C. §120 of U.S. patent application Ser.No. 14/357,832, filed May 13, 2014, which is based on PCT filingPCT/GB2012/053157 filed Dec. 17, 2012, and claims priority to BritishPatent Application 1121767.6, filed in the UK IPO Dec. 19, 2011, theentire contents of each of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to wireless telecommunications systems andmethods, and in particular to systems and methods for allocatingtransmission resources in wireless telecommunication systems.

Mobile communication systems have evolved over the past ten years or sofrom the GSM System (Global System for Mobile communications) to the 3Gsystem and now include packet data communications as well as circuitswitched communications. The third generation partnership project (3GPP)is developing a fourth generation mobile communication system referredto as Long Term Evolution (LTE) in which a core network part has beenevolved to form a more simplified architecture based on a merging ofcomponents of earlier mobile radio network architectures and a radioaccess interface which is based on Orthogonal Frequency DivisionMultiplexing (OFDM) on the downlink and Single Carrier FrequencyDivision Multiple Access (SC-FDMA) on the uplink.

Third and fourth generation mobile telecommunication systems, such asthose based on the 3GPP defined UMTS and Long Term Evolution (LTE)architectures, are able to support a more sophisticated range ofservices than simple voice and messaging services offered by previousgenerations of mobile telecommunication systems.

For example, with the improved radio interface and enhanced data ratesprovided by LTE systems, a user is able to enjoy high data rateapplications such as mobile video streaming and mobile videoconferencing that would previously only have been available via a fixedline data connection. The demand to deploy third and fourth generationnetworks is therefore strong and the coverage area of these networks,i.e. geographic locations where access to the networks is possible, isexpected to increase rapidly.

The anticipated widespread deployment of third and fourth generationnetworks has led to the parallel development of a class of devices andapplications which, rather than taking advantage of the high data ratesavailable, instead take advantage of the robust radio interface andincreasing ubiquity of the coverage area. Examples include so-calledmachine type communication (MTC) applications, some of which are in somerespects typified by semi-autonomous or autonomous wirelesscommunication devices (i.e. MTC devices) communicating small amounts ofdata on a relatively infrequent basis. Examples include so-called smartmeters which, for example, are located in a customer's home andperiodically transmit data back to a central MTC server relating to thecustomer's consumption of a utility such as gas, water, electricity andso on. Further information on characteristics of MTC-type devices can befound, for example, in the corresponding standards, such as ETSI TS 122368 V10.530 (2011-07)/3GPP TS 22.368 version 10.5.0 Release 10) [1].

Whilst it can be convenient for a terminal such as an MTC-type terminalto take advantage of the wide coverage area provided by a third orfourth generation mobile telecommunication network there are at presentdisadvantages. Unlike a conventional third or fourth generation mobileterminal such as a smartphone, a primary driver for MTC-type terminalswill be a desire for such terminals to be relatively simple andinexpensive. The type of functions typically performed by an MTC-typeterminal (e.g. simple collection and reporting of relatively smallamounts of data) do not require particularly complex processing toperform, for example, compared to a smartphone supporting videostreaming. However, third and fourth generation mobile telecommunicationnetworks typically employ advanced data modulation techniques andsupport wide bandwidth usage on the radio interface which can requiremore complex and expensive radio transceivers to implement. It isusually justified to include such complex transceivers in a smartphoneas a smartphone will typically require a powerful processor to performtypical smartphone type functions. However, as indicated above, there isnow a desire to use relatively inexpensive and less complex deviceswhich are nonetheless able to communicate using LTE-type networks.

With this in mind there has been proposed a concept of so-called“virtual carriers” operating within the bandwidth of a “host carrier”,for example, as described in co-pending UK patent applications numberedGB 1101970.0 [2], GB 1101981.7 [3], GB 1101966.8 [4], GB 1101983.3 [5],GB 1101853.8 [6], GB 1101982.5 [7], GB 1101980.9 [8] and GB 1101972.6[9]. A main principle underlying the concept of a virtual carrier isthat a frequency sub-region within a wider bandwidth host carrier isconfigured for use as a self-contained carrier, for example includingall control signalling within the frequency sub region. An advantage ofthis approach is to provide a carrier for use by low-capability terminaldevices capable of operating over only relatively narrow bandwidths.This allows devices to communicate on LTE-type networks, withoutrequiring the devices to support full bandwidth operation. By reducingthe bandwidth of the signal that needs to be decoded, the front endprocessing requirements (e.g., FFT, channel estimation, subframebuffering etc.) of a device configured to operate on a virtual carrierare reduced since the complexity of these functions is generally relatedto the bandwidth of the signal received.

There are, however, some potential drawbacks with some implementationsof the “virtual carrier” approach. For example, in accordance with someproposed approaches the available spectrum is hard partitioned betweenthe virtual carrier and the host carrier. This hard partitioning can beinefficient for a number of reasons. For example, the peak data ratethat can be supported by high-rate legacy devices is reduced becausehigh-rate devices can only be scheduled a portion of the bandwidth (andnot the whole bandwidth). Also, when the bandwidth is partitioned inthis way there can be a loss of trunking efficiency (there is astatistical multiplexing loss).

What is more, in some respects the virtual carrier approach represents arelatively significant departure from the current operating principlesfor LTE-type networks. This means relatively substantial changes to thecurrent standards would be required to incorporate the virtual carrierconcept into the LTE standards framework, thereby increasing thepractical difficulty of rolling out these proposed implementations.

Another proposal for reducing the required complexity of devicesconfigured to communicate over LTE-type networks is proposed in thediscussion document R1-113113 from Pantech submitted for the 3GPPTSG-RAN WG1 #66bis meeting in Zhuhai, China, 10 Oct. 2011 to 14 Oct.2011 [10]. The proposal is for low-complexity terminal devices to beallocated a limited number of physical resource blocks as compared to adevice with is fully LTE-compliant. This scheduling restriction meansterminal devices can implement their turbo decoding function moresimply, thereby reducing the processing complexity required. However,while this can be helpful in reducing the processing capability requiredfor turbo decoding, significant amounts of a device's processingrequirements are associated with front-end digital signal processingfunctions prior to turbo decoding. Such front-end digital signalprocessing functions include, for example, FFT/IFFT (fast Fouriertransform/inverse fast Fourier transform), channel estimation,equalization, digital filtering, etc.

Accordingly, there remains a desire for approaches which allowrelatively inexpensive and low complexity devices to communicate usingLTE-type networks.

SUMMARY OF THE INVENTION

According to an aspect of the invention there is provided a method ofoperating a base station for communicating data with a terminal devicein a wireless telecommunications system using a plurality ofsub-carriers spanning a system frequency band, the method comprising:transmitting physical-layer control information for the terminal deviceusing sub-carriers selected from across the system frequency band; andtransmitting higher-layer data for the terminal device usingsub-carriers selected from within a predetermined restricted frequencyband, wherein the restricted frequency band is smaller than and withinthe system frequency band.

In accordance with some embodiments the restricted frequency band isdefined by a standard of the wireless telecommunications system.

In accordance with some embodiments the method further comprisescommunicating with the terminal device to share an indication of therestricted frequency band.

In accordance with some embodiments the indication of the restrictedfrequency band is communicated during a connection establishmentprocedure in which a connection is established between the base stationand the terminal device.

In accordance with some embodiments the indication of the restrictedfrequency band is communicated using Radio Resource Control, RRC,signalling.

In accordance with some embodiments the indication of the restrictedfrequency band is communicated in association with a System InformationBlock, SIB, of the wireless telecommunications system.

In accordance with some embodiments the indication of the restrictedfrequency band is communicated using a radio resource that is defined bya standard of the wireless telecommunications system.

In accordance with some embodiments the method further comprisescommunicating with the terminal device to share an indication of a radioresource to be used for communicating the indication of the restrictedfrequency band.

In accordance with some embodiments the indication of the radio resourceis communicated during a connection establishment procedure in which aconnection is established between the base station and the terminaldevice.

In accordance with some embodiments the indication of the radio resourceis communicated in association with a Master Information Block, MIB, ofthe wireless telecommunications system.

In accordance with some embodiments the indication of the radio resourceis communicated using a physical broadcast channel of the wirelesstelecommunications system.

In accordance with some embodiments the indication of the radio resourceis communicated by the base station transmitting physical-layer controlinformation having a format selected to provide the indication of theradio resource.

In accordance with some embodiments the physical-layer controlinformation of the pre-defined format is transmitted on a physicaldownlink control channel of the wireless telecommunications system.

In accordance with some embodiments the physical-layer controlinformation for the terminal devices comprise an indication oftransmission resource allocations for the higher-layer data for theterminal device.

In accordance with some embodiments the physical-layer controlinformation for the terminal device is transmitted on a physicaldownlink control channel of the wireless telecommunications system.

In accordance with some embodiments the higher-layer data for theterminal device is transmitted on a physical downlink shared channel ofthe wireless telecommunications system.

According to an aspect of the invention there is provided a method ofoperating a base station for communicating data with terminal devices ina wireless telecommunications system using radio subframes comprising aplurality of symbols, the method comprising: transmitting physical-layercontrol information from the base station to a first terminal device andto a second terminal device using a first group of the symbols in aradio subframe; transmitting higher-layer data from the base station tothe first terminal device using a second group of the symbols in theradio subframe; and transmitting higher-layer data from the base stationto the second terminal device using a third group of the symbols in theradio subframe, wherein the number of symbols in the third group isfewer than the number of symbols in the second group.

According to an aspect of the invention there is provided a base stationfor communicating data with terminal devices in a wirelesstelecommunications system using a plurality of sub-carriers spanning asystem frequency band, wherein the base station is configured to:transmit physical-layer control information for a terminal device usingsub-carriers selected from across the system frequency band; andtransmit higher-layer data for the terminal device using sub-carriersselected from within a predetermined restricted frequency band, whereinthe restricted frequency band is smaller than and within the systemfrequency band.

In accordance with some embodiments the restricted frequency band isdefined by a standard of the wireless telecommunications system.

In accordance with some embodiments the base station is configured tocommunicate with the terminal device to share an indication of therestricted frequency band.

In accordance with some embodiments the base station is configured suchthat the indication of the restricted frequency band is communicatedduring a connection establishment procedure in which a connection isestablished between the base station and the terminal device.

In accordance with some embodiments the base station is configured suchthat the indication of the restricted frequency band is communicatedusing Radio Resource Control, RRC, signalling.

In accordance with some embodiments the base station is configured suchthat the indication of the restricted frequency band is communicated inassociation with a System Information Block, SIB, of the wirelesstelecommunications system.

In accordance with some embodiments the base station is configured suchthat the indication of the restricted frequency band is communicatedusing a radio resource that is defined by a standard of the wirelesstelecommunications system.

In accordance with some embodiments the base station is configured tocommunicate with the terminal device to share an indication of a radioresource to be used for communicating the indication of the restrictedfrequency band.

In accordance with some embodiments the base station is configured suchthat the indication of the radio resource is communicated during aconnection establishment procedure in which a connection is establishedbetween the base station and the terminal device.

In accordance with some embodiments the base station is configured suchthat the indication of the radio resource is communicated in associationwith a Master Information Block, MIB, of the wireless telecommunicationssystem.

In accordance with some embodiments the base station is configured suchthat the indication of the radio resource is communicated using aphysical broadcast channel of the wireless telecommunications system.

In accordance with some embodiments the base station is configured suchthat the indication of the radio resource is communicated bytransmitting physical-layer control information having a format selectedto provide the indication of the radio resource.

In accordance with some embodiments the base station is configured totransmit the physical-layer control information of the pre-definedformat on a physical downlink control channel of the wirelesstelecommunications system.

In accordance with some embodiments the physical-layer controlinformation for the terminal device comprises an indication oftransmission resource allocations for the higher-layer data for theterminal device.

In accordance with some embodiments the base station is configured totransmit the physical-layer control information for the terminal deviceon a physical downlink control channel of the wirelesstelecommunications system.

In accordance with some embodiments the base station is configured totransmit the higher-layer data for the terminal device on a physicaldownlink shared channel of the wireless telecommunications system.

According to an aspect of the invention there is provided a base stationfor communicating data with terminal devices in a wirelesstelecommunications system using radio subframes comprising a pluralityof symbols, wherein the base station is configured to: transmitphysical-layer control information from the base station to a firstterminal device and to a second terminal device using a first group ofthe symbols in a radio subframe; transmit higher-layer data from thebase station to the first terminal device using a second group of thesymbols in the radio subframe; and transmit higher-layer data from thebase station to the second terminal device using a third group of thesymbols in the radio subframe, wherein the number of symbols in thethird group is fewer than the number of symbols in the second group.

According to an aspect of the invention there is provided a systemcomprising a base station in accordance with any of the above-mentionedaspects of the invention and a terminal device.

According to an aspect of the invention there is provided a method ofoperating a terminal device for receiving data from a base station in awireless telecommunications system using a plurality of sub-carriersspanning a system frequency band, the method comprising: receiving andbuffering physical-layer control information transmitted by the basestation on sub-carriers spanning the system frequency band; receivingand buffering higher-layer data transmitted by the base station onsub-carriers spanning a predetermined restricted frequency band, whereinthe restricted frequency band is smaller than and within the systemfrequency band; processing the buffered physical-layer controlinformation to determine an allocation of higher-layer data for theterminal device within the restricted frequency band; and processing thebuffered higher-layer data to extract the allocation of higher-layerdata for the terminal device from the restricted frequency band.

It will be appreciated that receiving and buffering physical-layercontrol information may in general involve receiving and bufferingtransmission resources that carry the physical-layer controlinformation. For example, the transmission resources may be resourceelements containing physical-layer control information. A resourceelement may, for example in an LTE-type network, comprise a subcarrieron a single symbol. In this context a resource element may thus transmita single modulation symbol (i.e. a single QPSK/16QAM/64QAM modulationsymbol). It will similarly be appreciated that receiving and bufferinghigher-layer data may in general involve receiving and bufferingtransmission resources that carry higher-layer data.

In accordance with some embodiments the restricted frequency band isdefined by a standard of the wireless telecommunications system.

In accordance with some embodiments the method further comprisescommunicating with the base station to share an indication of therestricted frequency band.

In accordance with some embodiments the indication of the restrictedfrequency band is communicated during a connection establishmentprocedure in which a connection is established between the terminaldevice and the base station.

In accordance with some embodiments the indication of the restrictedfrequency band is communicated using Radio Resource Control, RRC,signalling.

In accordance with some embodiments the indication of the restrictedfrequency band is communicated in association with a System InformationBlock, SIB, of the wireless telecommunications system.

In accordance with some embodiments the indication of the restrictedfrequency band is communicated using a radio resource that is defined bya standard of the wireless telecommunications system.

In accordance with some embodiments the method further comprisescommunicating with the base station to share an indication of a radioresource to be used for communicating the indication of the restrictedfrequency band.

In accordance with some embodiments the indication of the radio resourceis communicated during a connection establishment procedure in which aconnection is established between the terminal device and the basestation.

In accordance with some embodiments the indication of the radio resourceis communicated in association with a Master Information Block, MTB, ofthe wireless telecommunications system.

In accordance with some embodiments the indication of the radio resourceis communicated using a physical broadcast channel of the wirelesstelecommunications system.

In accordance with some embodiments the indication of the radio resourceis received by the terminal device as physical-layer control informationhaving a format selected by the base station to provide the indicationof the radio resource.

In accordance with some embodiments the physical-layer controlinformation of the pre-defined format is received by the terminal on aphysical downlink control channel of the wireless telecommunicationssystem.

In accordance with some embodiments the physical-layer controlinformation comprises an indication of transmission resource allocationsfor the higher-layer data.

In accordance with some embodiments the physical-layer controlinformation is received on a physical downlink control channel of thewireless telecommunications system.

In accordance with some embodiments the higher-layer data is received ona physical downlink shared channel of the wireless telecommunicationssystem.

According to an aspect of the invention there is provided a method ofoperating a mobile device for receiving data in a wirelesstelecommunications system using radio subframes comprising a pluralityof symbols, the method comprising: receiving and bufferingphysical-layer control information transmitted by the base station usinga first group of the symbols in a radio subframe; receiving andbuffering higher-layer data transmitted by the base station using asecond group of the symbols of the radio subframe, wherein the number ofthe symbols in the second group is less than the number of the symbolsof the subframe available for transmitting higher-layer data to otherterminal devices; processing the buffered physical-layer controlinformation to determine an allocation of higher-layer data for theterminal device within the second group of the symbols in the subframe;and processing the buffered higher-layer data to extract the allocationof higher-layer data for the terminal device from the second group ofthe symbols in the subframe.

According to an aspect of the invention there is provided a mobileterminal for receiving data from a base station in a wirelesscommunications system using a plurality of sub-carriers spanning asystem frequency band, wherein the mobile terminal is configured to:receive and buffer physical-layer control information transmitted by thebase station on sub-carriers spanning the system frequency band; receiveand buffer higher-layer data transmitted by the base station onsub-carriers spanning a predetermined restricted frequency band, whereinthe restricted frequency band is smaller than and within the systemfrequency band; process the buffered physical-layer control informationto determine an allocation of higher-layer data for the terminal devicewithin the restricted frequency band; and process the bufferedhigher-layer data to extract the allocation of higher-layer data for theterminal device from the restricted frequency band.

In accordance with some embodiments the restricted frequency band isdefined by a standard of the wireless telecommunications system.

In accordance with some embodiments the mobile terminal is configured tocommunicate with the base station to share an indication of therestricted frequency band.

In accordance with some embodiments the mobile terminal is configuredsuch that the indication of the restricted frequency band iscommunicated during a connection establishment procedure in which aconnection is established between the mobile terminal and the basestation.

In accordance with some embodiments the mobile terminal is configuredsuch that the indication of the restricted frequency band iscommunicated using Radio Resource Control, RRC, signalling.

In accordance with some embodiments the mobile terminal is configuredsuch that the indication of the restricted frequency band iscommunicated in association with a System Information Block, SIB, of thewireless telecommunications system.

In accordance with some embodiments the mobile terminal is configuredsuch that the indication of the restricted frequency band iscommunicated using a radio resource that is defined by a standard of thewireless telecommunications system.

In accordance with some embodiments the mobile terminal is configured tocommunicate with the base station to share an indication of a radioresource to be used for communicating the indication of the restrictedfrequency band.

In accordance with some embodiments the mobile terminal is configuredsuch that the indication of the radio resource is communicated during aconnection establishment procedure in which a connection is establishedbetween the mobile terminal and the base station.

In accordance with some embodiments the mobile terminal is configuredsuch that the indication of the radio resource is communicated inassociation with a Master Information Block, MIB, of the wirelesstelecommunications system.

In accordance with some embodiments the mobile terminal is configuredsuch that the indication of the radio resource is communicated using aphysical broadcast channel of the wireless telecommunications system.

In accordance with some embodiments the mobile terminal is configuredsuch that the indication of the radio resource is received bytransmitting physical-layer control information having a format selectedto provide the indication of the radio resource.

In accordance with some embodiments the mobile terminal is configured toreceive the indication of the radio resource as physical-layer controlinformation having a format selected by the base station to provide theindication of the radio resource.

In accordance with some embodiments the physical-layer controlinformation for the terminal device comprises an indication oftransmission resource allocations for the higher-layer data.

In accordance with some embodiments the mobile terminal is configured toreceive the physical-layer control information on a physical downlinkcontrol channel of the wireless telecommunications system.

In accordance with some embodiments the mobile terminal is configured toreceive the higher-layer data on a physical downlink shared channel ofthe wireless telecommunications system.

According to an aspect of the invention there is provided a mobileterminal for communicating data with a base station in a wirelesstelecommunications system using radio subframes comprising a pluralityof symbols, wherein the mobile terminal is configured to: receive andbuffer physical-layer control information transmitted by the basestation using a first group of the symbols in a radio subframe; receiveand buffer higher-layer data transmitted by the base station using asecond group of the symbols of the radio subframe, wherein the number ofthe symbols in the second group is less than the number of the symbolsof the subframe available for transmitting higher-layer data to otherterminal devices; process the buffered physical-layer controlinformation to determine an allocation of higher-layer data for theterminal device within the second group of the symbols in the subframe;and process the buffered higher-layer data to extract the allocation ofhigher-layer data for the terminal device from the second group of thesymbols in the subframe.

According to an aspect of the invention there is provided a systemcomprising a base station and a terminal device in accordance with anyof the above-mentioned aspects of the invention.

It will be appreciated that features and aspects of the inventiondescribed above in relation to the first and other aspects of theinvention are equally applicable and may be combined with embodiments ofthe invention according to the different aspects of the invention asappropriate, and not just in the specific combinations described above.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings where likeparts are provided with corresponding reference numerals and in which:

FIG. 1 provides a schematic diagram illustrating an example of aconventional mobile telecommunication system;

FIG. 2 provides a schematic diagram illustrating a conventional LTEradio frame;

FIG. 3 provides a schematic diagram illustrating an example of aconventional LTE downlink radio subframe,

FIG. 4 provides a schematic diagram illustrating a conventional LTE“camp-on” procedure;

FIG. 5 schematically represents a wireless telecommunications systemaccording to an embodiment of the invention;

FIG. 6 schematically represents two arbitrary downlink subframes as seenby a conventional terminal device operating in the wirelesstelecommunications system of FIG. 5;

FIG. 7 schematically represents two arbitrary downlink subframes as seenby a terminal device operating according to an embodiment of theinvention in the wireless telecommunications system of FIG. 5;

FIG. 8 is a flow diagram schematically representing a method for aterminal device operating according to an embodiment of the inventionattaching to the wireless telecommunications system of FIG. 5;

FIG. 9 schematically represents two arbitrary downlink subframes as seenby a terminal device operating according to another embodiment of theinvention in a wireless telecommunications system according to anembodiment of the invention.

DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 provides a schematic diagram illustrating some basicfunctionality of a mobile telecommunications network/system 100operating in accordance with LTE principles and which may be adapted toimplement embodiments of the invention as described further below.Various elements of FIG. 1 and their respective modes of operation arewell-known and defined in the relevant standards administered by the3GPP (RTM) body and also described in many books on the subject, forexample, Holma H. and Toskala A [11]. It will be appreciated thatoperational aspects of the telecommunications network which are notspecifically described below may be implemented in accordance with anyknown techniques, for example according to the relevant standards.

The network 100 includes a plurality of base stations 101 connected to acore network 102. Each base station provides a coverage area 103 (i.e. acell) within which data can be communicated to and from terminal devices104. Data is transmitted from base stations 101 to terminal devices 104within their respective coverage areas 103 via a radio downlink. Data istransmitted from terminal devices 104 to the base stations 101 via aradio uplink. The core network 102 routes data to and from the terminaldevices 104 via the respective base stations 101 and provides functionssuch as authentication, mobility management, charging and so on.Terminal devices may also be referred to as mobile stations, userequipment (UE), user terminal, mobile radio, and so forth. Base stationsmay also be referred to as transceiver stations/nodeBs/e-nodeBs, and soforth.

Mobile telecommunications systems such as those arranged in accordancewith the 3GPP defined Long Term Evolution (LTE) architecture use anorthogonal frequency division modulation (OFDM) based interface for theradio downlink (so-called OFDMA) and a single carrier frequency divisionmultiple access scheme (SC-FDMA) on the radio uplink. FIG. 2 shows aschematic diagram illustrating an OFDM based LTE downlink radio frame201. The LTE downlink radio frame is transmitted from an LTE basestation (known as an enhanced Node B) and lasts 10 ms. The downlinkradio frame comprises ten subframes, each subframe lasting 1 ms. Aprimary synchronisation signal (PSS) and a secondary synchronisationsignal (SSS) are transmitted in the first and sixth subframes of the LTEframe. A physical broadcast channel (PBCH) is transmitted in the firstsubframe of the LTE frame.

FIG. 3 is a schematic diagram of a grid which illustrates the structureof an example conventional downlink LTE subframe. The subframe comprisesa predetermined number of symbols which are transmitted over a 1 msperiod. Each symbol comprises a predetermined number of orthogonalsub-carriers distributed across the bandwidth of the downlink radiocarrier.

The example subframe shown in FIG. 3 comprises 14 symbols and 1200sub-carriers spread across a 20 MHz bandwidth and is the first subframein a frame (hence it contains PBCH). The smallest allocation of physicalresource for transmission in LTE is a resource block comprising twelvesub-carriers transmitted over one subframe. For clarity, in FIG. 3, eachindividual resource element is not shown, instead each individual box inthe subframe grid corresponds to twelve sub-carriers transmitted on onesymbol.

FIG. 3 shows in hatching resource allocations for four LTE terminals340, 341, 342, 343. For example, the resource allocation 342 for a firstLTE terminal (UE1) extends over five blocks of twelve sub-carriers (i.e.60 sub-carriers), the resource allocation 343 for a second LTE terminal(UE2) extends over six blocks of twelve sub-carriers (i.e. 72sub-carriers) and so on.

Control channel data is transmitted in a control region 300 (indicatedby dotted-shading in FIG. 3) of the subframe comprising the first nsymbols of the subframe where n can vary between one and three symbolsfor channel bandwidths of 3 MHz or greater and where n can vary betweentwo and four symbols for a channel bandwidth of 1.4 MHz. For the sake ofproviding a concrete example, the following description relates to hostcarriers with a channel bandwidth of 3 MHz or greater so the maximumvalue of n will be 3 (as in the example of FIG. 3). The data transmittedin the control region 300 includes data transmitted on the physicaldownlink control channel (PDCCH), the physical control format indicatorchannel (PCFICH) and the physical HARQ indicator channel (PHICH). Thesechannels transmit physical layer control information.

PDCCH contains control data indicating which sub-carriers of thesubframe have been allocated to specific LTE terminals. This may bereferred to as physical-layer control signalling/data. Thus, the PDCCHdata transmitted in the control region 300 of the subframe shown in FIG.3 would indicate that UE1 has been allocated the block of resourcesidentified by reference numeral 342, that UE2 has been allocated theblock of resources identified by reference numeral 343, and so on.

PCFICH contains control data indicating the size of the control region(i.e. between one and three symbols for channel bandwiths of 3 MHz orgreater).

PHICH contains HARQ (Hybrid Automatic Request) data indicating whetheror not previously transmitted uplink data has been successfully receivedby the network.

Symbols in a central band 310 of the time-frequency resource grid areused for the transmission of information including the primarysynchronisation signal (PSS), the secondary synchronisation signal (SSS)and the physical broadcast channel (PBCH). This central band 310 istypically 72 sub-carriers wide (corresponding to a transmissionbandwidth of 1.08 MHz). The PSS and SSS are synchronisation signals thatonce detected allow an LTE terminal device to achieve framesynchronisation and determine the physical layer cell identity of theenhanced Node B transmitting the downlink signal. The PBCH carriesinformation about the cell, comprising a master information block (MIB)that includes parameters that LTE terminals use to properly access thecell. Data transmitted to individual LTE terminals on the physicaldownlink shared channel (PDSCH) can be transmitted in other resourceelements of the subframe. In general PDSCH conveys a combination ofuser-plane data and non-physical layer control-plane data (such as RadioResource Control (RRC) and Non Access Stratum (NAS) signalling). Theuser-plane data and non-physical layer control-plane data conveyed onPDSCH may be referred to as higher layer data (i.e. data associated witha layer higher than the physical layer).

FIG. 3 also shows a region of PDSCH containing system information andextending over a bandwidth of R₃₄₄. A conventional LTE subframe willalso include reference signals which are discussed further below but notshown in FIG. 3 in the interests of clarity.

The number of sub-carriers in an LTE channel can vary depending on theconfiguration of the transmission network. Typically this variation isfrom 72 sub carriers contained within a 1.4 MHz channel bandwidth to1200 sub-carriers contained within a 20 MHz channel bandwidth (asschematically shown in FIG. 3). As is known in the art, data transmittedon the PDCCH, PCFICH and PHICH is typically distributed on thesub-carriers across the entire bandwidth of the subframe to provide forfrequency diversity. Therefore a conventional LTE terminal must be ableto receive the entire channel bandwidth in order to receive and decodethe control region.

FIG. 4 illustrates an LTE “camp-on” process, that is, the processfollowed by a terminal so that it can decode downlink transmissionswhich are sent by a base station via a downlink channel. Using thisprocess, the terminal can identify the parts of the transmissions thatinclude system information for the cell and thus decode configurationinformation for the cell.

As can be seen in FIG. 4, in a conventional LTE camp-on procedure, theterminal first synchronizes with the base station (step 400) using thePSS and SSS in the centre band and then decodes the PBCH (step 401).Once the terminal has performed steps 400 and 401, it is synchronizedwith the base station.

For each subframe, the terminal then decodes the PCFICH which isdistributed across the entire bandwidth of carrier 320 (step 402). Asdiscussed above, an LTE downlink carrier can be up to 20 MHz wide (1200sub-carriers) and a standard LTE-compliant terminal therefore has tohave the capability to receive and decode transmissions on a 20 MHzbandwidth in order to decode the PCFICH. Accordingly, at the PCFICHdecoding stage, with a 20 MHz carrier band, the terminal operates at alarger bandwidth (bandwidth of R₃₂₀) than during steps 400 and 401(bandwidth of R₃₁₀) relating to synchronization and PBCH decoding.

The terminal then ascertains the PH1CH locations (step 403) and decodesthe PDCCH (step 404), in particular for identifying system informationtransmissions and for identifying its personal allocation grants. Theallocation grants are used by the terminal to locate system informationand to locate its data in the PDSCH. Both system information andpersonal allocations are transmitted on PDSCH and scheduled within thecarrier band 320. Steps 403 and 404 also require a standardLTE-compliant terminal to operate on the entire bandwidth R₃₂₀ of thecarrier band.

At steps 402 to 404, the terminal decodes information contained in thecontrol region 300 of a subframe. As explained above, in LTE, the threecontrol channels mentioned above (PCFICH, PH1CH and PDCCH) can be foundacross the control region 300 of the carrier where the control regionextends over the range R₃₂₀ and occupies the first one, two or threeOFDM symbols of each subframe as discussed above. In a subframe,typically the control channels do not use all the resource elementswithin the control region 300, but they are scattered across the entireregion, such that an LTE terminal has to be able to simultaneouslyreceive the entire control region 300 for decoding each of the threecontrol channels.

The terminal can then decode the PDSCH (step 405) which contains systeminformation or data transmitted for this terminal.

As explained above, in an LTE subframe the PDSCH generally occupiesgroups of resource elements which are neither in the control region norin the resource elements occupied by PSS, SSS or PBCH. The data in theblocks of resource elements 340, 341, 342, 343 allocated to thedifferent mobile communication terminals (UEs) shown in FIG. 3 have asmaller bandwidth than the bandwidth of the entire carrier, although todecode these blocks a terminal first receives the PDCCH spread acrossthe frequency range R₃₂₀ to determine if the PDCCH indicates that aPDSCH resource is allocated to the UE and should be decoded. Once a UEhas received the entire subframe, it can then decode the PDSCH in therelevant frequency range (if any) indicated by the PDCCH. So forexample, UE1 discussed above decodes the whole control region 300 todetermine its resource allocation and then extracts the relevant datafrom the corresponding resource block 342.

FIG. 5 schematically shows a telecommunications system 500 according toan embodiment of the invention. The telecommunications system 500 inthis example is based broadly on an LTE-type architecture. As such manyaspects of the operation of the telecommunications system 500 arestandard and well understood and not described here in detail in theinterest of brevity. Operational aspects of the telecommunicationssystem 500 which are not specifically described herein may beimplemented in accordance with any known techniques, for exampleaccording to the LTE-standards.

The telecommunications system 500 comprises a core network part (evolvedpacket core) 502 coupled to a radio network part. The radio network partcomprises a base station (evolved-nodeB) 504, a first terminal device506 and a second terminal device 508. It will of course be appreciatedthat in practice the radio network part may comprise a plurality of basestations serving a larger number of terminal devices across variouscommunication cells. However, only a single base station and twoterminal devices are shown in FIG. 5 in the interests of simplicity.

As with a conventional mobile radio network, the terminal devices 506,508 are arranged to communicate data to and from the base station(transceiver station) 504. The base station is in turn communicativelyconnected to a serving gateway, S-GW, (not shown) in the core networkpart which is arranged to perform routing and management of mobilecommunications services to the terminal devices in thetelecommunications system 500 via the base station 504. In order tomaintain mobility management and connectivity, the core network part 502also includes a mobility management entity (not shown) which manages theenhanced packet service, EPS, connections with the terminal devices 506,508 operating in the communications system based on subscriberinformation stored in a home subscriber server, HSS. Other networkcomponents in the core network (also not shown for simplicity) include apolicy charging and resource function, PCRF, and a packet data networkgateway, PDN-GW, which provides a connection from the core network part502 to an external packet data network, for example the Internet. Asnoted above, the operation of the various elements of the communicationssystem 500 shown in FIG. 5 may be broadly conventional apart from wheremodified to provide functionality in accordance with embodiments of theinvention as discussed herein.

In this example, it is assumed the first terminal device 506 is aconventional smart-phone type terminal device communicating with thebase station 504. Thus, and as is conventional, this first terminaldevice 504 comprises a transceiver unit 506 a for transmission andreception of wireless signals and a controller unit 506 b configured tocontrol the smart phone 506. The controller unit 506 b may comprise aprocessor unit which is suitably configured/programmed to provide thedesired functionality using conventional programming/configurationtechniques for equipment in wireless telecommunications systems. Thetransceiver unit 506 a and the controller unit 506 b are schematicallyshown in FIG. 5 as separate elements. However, it will be appreciatedthat the functionality of these units can be provided in variousdifferent ways, for example using a single suitably programmedintegrated circuit. As will be appreciated the smart phone 506 will ingeneral comprise various other elements associated with its operatingfunctionality.

In this example, it is assumed the second terminal device 508 is amachine-type communication (MTC) terminal device. As discussed above,these types of device may be typically characterised as semi-autonomousor autonomous wireless communication devices communicating small amountsof data. Examples include so-called smart meters which, for example, maybe located in a customer's house and periodically transmit informationback to a central MTC server data relating to the customer's consumptionof a utility such as gas, water, electricity and so on. MTC devices mayin some respects be seen as devices which can be supported by relativelylow bandwidth communication channels having relatively low quality ofservice (QoS), for example in terms of latency. It is assumed here theMTC terminal device 508 in FIG. 5 is such a device.

As with the smart phone 506, the MTC device 508 comprises a transceiverunit 508 a for transmission and reception of wireless signals and acontroller unit 508 b configured to control the MTC device 508. Thecontroller unit 508 b may comprise a processor unit which is suitablyconfigured/programmed to provide the desired functionality describedherein using conventional programming/configuration techniques forequipment in wireless telecommunications systems. The transceiver unit508 a and the controller unit 508 b are schematically shown in FIG. 5 asseparate elements for ease of representation. However, it will beappreciated that the functionality of these units can be provided invarious different ways following established practices in the art, forexample using a single suitably programmed integrated circuit. It willbe appreciated the MTC device 508 will in general comprise various otherelements associated with its operating functionality.

The base station 504 comprises a transceiver unit 504 a for transmissionand reception of wireless signals and a controller unit 504 b configuredto control the base station 504. The controller unit 504 b may comprisea processor unit which is suitably configured/programmed to provide thedesired functionality described herein using conventionalprogramming/configuration techniques for equipment in wirelesstelecommunications systems. The transceiver unit 504 a and thecontroller unit 504 b are schematically shown in FIG. 5 as separateelements for ease of representation. However, it will be appreciatedthat the functionality of these units can be provided in variousdifferent ways following established practices in the art, for exampleusing a single suitably programmed integrated circuit. It will beappreciated the base station 504 will in general comprise various otherelements associated with its operating functionality.

Thus, the base station 504 is configured to communicate data with thesmart phone 506 over a first radio communication link 510 andcommunicate data with the MTC device 508 over a second radiocommunication link 512.

It is assumed here the base station 504 is configured to communicatewith the smart phone 506 over the first radio communication link 510 inaccordance with the established principles of LTE-based communications.

FIG. 6 schematically represents two arbitrary downlink subframes(identified as subframe n and subframe n+1) as seen by the smart phone506 according to the established LTE standards as discussed above. Eachsubframe is in essence a simplified version of what is represented inFIG. 3. Thus, each subframe comprises a control region 600 supportingthe PCFICH, PHICH and PDCCH channels as discussed above and a PDSCHregion 602 for communicating higher-layer data (for example user-planedata and non-physical layer control-plane signalling) to respectiveterminal devices, such as the smart phone 506, as well as systeminformation, again as discussed above. For the sake of giving a concreteexample, the frequency bandwidth (BW) of the carrier with which thesubframes are associated is taken to be 20 MHz. Also schematically shownin FIG. 6 by black shading are example PDSCH downlink allocations 604for the smart phone 506. In accordance with the defined standards, andas discussed above, individual terminal devices derive their specificdownlink allocations for a subframe from PDCCH transmitted in thecontrol region 600 of the subframe. For the arbitrary example shown inFIG. 6, the smart phone 506 is allocated downlink resources spanning arelatively small fraction of the 20 MHz bandwidth near to the upper endof the carrier frequency in subframe n, and is allocated a largerfraction of the available 20 MHz bandwidth at a lower frequency insubframe n+1. The specific allocations of PDSCH resources for the smartphone are determined by a scheduler in the network based on the dataneeds for the device in accordance with standard techniques.

Although the smart phone 506 is typically only allocated a subset of theavailable PDSCH resources in any given subframe, the smart phone 506could be allocated these resources anywhere across the full PDSCHbandwidth (BW). Accordingly, the smart phone will in the first instancereceive and buffer the entire subframe. The smart phone 506 will thenprocess the subframe to decode PDCCH to determine what resources areallocated on PDSCH, and then process the data received during PDSCHsymbols and extracts the relevant higher-layer data therefrom.

Thus, referring to FIG. 6, the smart phone 506 represented in FIG. 5buffers for each subframe the entire control region 600 (shaded darkgrey in FIG. 6) and the entire PDSCH region 602 (transmitted in theresources contained in the areas shaded light grey and black in FIG. 6),and extracts the higher-layer data allocated to the smart phone(transmitted in the resources contained in the area shaded black in FIG.6) from the PDSCH region 602 based on allocation information conveyed inthe control region 600.

The inventor has recognised that the requirement for terminal devices tobuffer and process each complete subframe to identify and extract whatwill typically be only a small fraction of the total PDSCH resourcescontained in the subframe for the terminal device introduces asignificant processing overhead. Accordingly, the inventor has conceivedof approaches in accordance with which example embodiments of theinvention may allow for a terminal device, for example an MTC device, tooperate generally in accordance with the principles of existingnetworks, but without needing to buffer and process an entire subframeto identify and extract its own higher-layer data from that subframe.

This can be achieved in accordance with some embodiments of theinvention by pre-establishing a restricted frequency band within whichhigher-layer data, e.g. on PDSCH in LTE, may be communicated from a basestation to a terminal device, wherein the restricted frequency band isnarrower than the overall system frequency band (carrier bandwidth) usedfor communicating physical-layer control information, e.g. on PDCCH inLTE. Thus the base station may be configured to only allocate downlinkresources for the terminal device on PDSCH within the restrictedfrequency band. Because the terminal device knows in advance that itwill only be allocated PDSCH resources within the restricted frequencyband, the terminal device does not need to buffer and process any PDSCHresources from outside the pre-determined restricted frequency band.This principle is schematically shown in FIG. 7.

FIG. 7 schematically represents two arbitrary downlink subframes(identified as subframe n and subframe n+1) as seen by the MTC device508 according to an embodiment of the invention. FIG. 7 is in somerespects similar to FIG. 6, and aspects of FIG. 7 which directlycorrespond to aspects of FIG. 6 are not described again in detail.

In this example it is assumed the base station 504 and the MTC device508 have both pre-established that higher-layer data is to becommunicated from the base station to the MTC device only within arestricted frequency band defined by upper and lower frequencies f1# andf2# (having a bandwidth Δf). In this example the restricted frequencyband encompasses the central part of the overall system (carrier)frequency band BW. For the sake of a concrete example, the restrictedfrequency band is assumed here to have a bandwidth (Δf) of 1.4 MHz andto be centred on the overall system bandwidth (i.e. f1#=fc−Δf/2 andf2#=fc+Δf/2, where fc is the central frequency of the system frequencyband). There are various mechanisms by which the frequency band can beestablished/shared between a base station and terminal device and someof these are discussed further below.

FIG. 7 represents in shading the portions of each subframe for which theMTC device 508 is arranged to buffer resource elements ready forprocessing. The buffered part of each subframe comprises a controlregion 600 supporting conventional physical-layer control information,such as the PCFICH, PHICH and PDCCH channels as discussed above and arestricted PDSCH region 702. The physical-layer control regions 600 thatare buffered by the MTC device 508 are the same as the physical-layercontrol regions 600 buffered by the smart phone device 506 asrepresented in FIG. 6. However, the PDSCH regions 702 carryinghigher-layer data which are buffered by the MTC device 508 are smallerthan the PDSCH regions 602 buffered by the smart phone device 506 asrepresented in FIG. 6. This is possible because, as noted above, inaccordance with an embodiment of the invention, the base station 504 isadapted so that higher-layer data on PDSCH can be allocated to theterminal device 508 only on subcarriers within the restricted frequencyband f1# to f2#, and the MTC terminal device 508 “knows” this, and socan be configured to ignore (i.e. not buffer) PDSCH resources that areoutside the restricted frequency band within which the terminal devicemight potentially be allocated downlink resources.

Also schematically shown in FIG. 7 by black shading are example PDSCHdownlink allocations 704 for the MTC device 508 within the restrictedfrequency band. The MTC device 508 may be configured to derive itsspecific PDSCH downlink allocations 704 for each subframe from PDCCHtransmitted in the control region 600 of the subframe in accordance withthe defined standards. That is to say, the principles for communicatingto the MTC device 508 the downlink allocations 704 it has been allocatedwithin the restricted frequency band does not need modifying toimplement an embodiment of the invention. The MTC device 508 willtypically only be allocated a subset of the PDSCH resources within therestricted frequency band in any given subframe, although in accordancewith an embodiment of the invention, the MTC device 508 could beallocated these resources anywhere across the restricted frequency band.Accordingly, the MTC device will in the first instance receive andbuffer the entire control region 600 and the entire restricted frequencyband 702 in a subframe. The MTC device 508 will then process the controlregion to decode PDCCH to determine what resources are allocated onPDSCH within the restricted frequency band, and then process the databuffered during PDSCH symbols within the restricted frequency band andextract the relevant higher-layer data therefrom.

Thus, referring to FIG. 7, the MTC device 508 represented in FIG. 5buffers for each subframe the entire control region 600 (transmitted inthe resources contained in the area shaded dark grey in FIG. 7) and therestricted frequency band PDSCH region 702 (transmitted in the resourcescontained in the area shaded light grey and black in FIG. 7), andextracts the higher-layer data allocated to the MTC device (transmittedin the resources contained in the area shaded black in FIG. 7) from therestricted PDSCH regions 702 based on allocation information conveyed inthe control region 600.

In one example LTE-based implementation of an embodiment of theinvention each subframe is taken to comprise 14 symbols (timeslots) withPDCCH transmitted on the first three symbols and PDSCH is transmitted onthe remaining 11 symbols. Furthermore, the wireless telecommunicationssystem is taken in this example to operate over a system frequency bandof 20 MHz (100 resource blocks) with a pre-established restrictedfrequency band of 1.4 MHz (six resource blocks) defined forcommunicating with the terminal devices operating in accordance with anembodiment of the invention.

In this case, a conventional terminal device, such as the smart phone506 shown in FIG. 5, is required to buffer a region of 100 resourceblocks (20 MHz) by 14 symbols, which is 1400 elements. However, aterminal device according to an embodiment of the invention, such as theMTC device 508 shown in FIG. 5, might only buffer the control region,which is 100 resource blocks (20 MHz) by 3 symbols, and the restrictedPDSCH region, which is 6 resource blocks (1.4 MHz) by 11 symbols.Accordingly, a terminal device operating in accordance with this exampleembodiment of the invention buffers a total of (100×3)+(6×11)=366elements. This is significantly less than (by around a factor of four)the 1400 elements buffered by a conventional device. This hasadvantageous consequences in terms of reduced memory and processingcapacity requirements, e.g. in terms of channel estimation processing,for the terminal device receiving higher-layer data only within therestricted frequency band. Consequently, terminal devices having reducedcapacity as compared to the minimum requirements of a conventionalterminal device can be supported in the network. Furthermore, bymaintaining full system frequency band operation for the physical-layercontrol information (which is used by all terminal devices), a terminaldevice can operate in accordance with an embodiment of the invention ina wireless communication system that also supports conventional terminaldevices in a manner which is transparent to the conventional terminaldevices.

It will of course be appreciated that the specific numerical parametersused here are provided purely for the sake of concrete example, andother implementations of the invention may adopt other parameters, forexample different bandwidths and locations for the restricted frequencyband.

There are a number of different ways in which information on therestricted frequency band can be established by/shared between the basestation and terminal device.

In some cases the restricted frequency band may be standardised withinthe wireless communications system. For example, it may be decided thatany terminal device and base station which are to operate within thewireless communication system in accordance with an implementation of anembodiment of the invention should assume a restricted frequency bandthat has a bandwidth of 1.4 MHz and a location at the centre of thesystem frequency band. (Of course other parameters could be defined, forexample defining lower and upper frequency limits for the standardisedrestricted frequency bandwidth instead of a central frequency andbandwidth). This provides a simple approach, but with limitedflexibility. It will be appreciated that a restricted frequency band maybe established by the base station and terminal device in various waysbased on pre-defined standards. For example, rather than explicitlydefine the restricted frequency range, a mechanism for deriving a rangemay be defined in relevant standards. For example, the standards mayspecify that all terminal devices are to assume a given bandwidth forthe restricted frequency band and to derive a location for therestricted frequency band from an identifier that is known to both thebase station and the terminal device. For example, in a simpleimplementation terminal devices associated with an odd-numbered IMSI mayassume a first location for the restricted frequency band while terminaldevices associated with an even IMSI may assume a second location forthe restricted frequency band. This provides for multiple restrictedfrequency bands to be provided based on pre-defined standards so that agreater number of reduced-capacity terminal devices may be allocated inany given subframe.

However, to improve overall scheduling flexibility it may be preferablein some implementations for the restricted frequency band to be selectedby the base station and conveyed to the terminal device in advance, forexample during a cell-attach procedure. The operating capabilities ofthe terminal device will typically set some limits on the restrictedfrequency band that may be used. For example a given terminal device maybe unable to operate using a restricted frequency band having abandwidth above some threshold. This may be accounted for bystandardisation, for example by limiting the maximum bandwidth that maybe established by the base station for the restricted frequency band, orbased on the exchange of capability messages between the base stationand terminal device.

A base station may, for example, be configured to communicateinformation regarding the restricted frequency band which is to be usedfor communicating with a reduced-capacity terminal device using RRC(radio resource control) signalling. Some examples of how this may beachieved are now described in the context of an LTE-based implementationof an embodiment of the invention. Here it is assumed a reduced-capacityterminal device only has capacity to buffer and process the controlregion and a 1.4 MHz wide restricted frequency band of the PDSCH regionin each subframe it receives.

In accordance with this example embodiment it is assumed thereduced-capacity terminal device seeks to connect to a base stationfollowing broadly conventional cell-attach procedures, such as shown inFIG. 4 and discussed above. Thus, the reduced-capacity terminal deviceinitially receives synchronisation signals and decodes PBCH usingbroadly conventional techniques. The terminal device is able to do thisbecause, as shown in FIG. 3, the locations of the synchronisationsignals and PBCH are defined and fixed, and furthermore they span afrequency range that the terminal device is able to buffer and process.Accordingly, the terminal device can achieve synchronisation and readPBCH using broadly conventional techniques. This allows the terminaldevice to derive information carried in the Master Information Block(MIB), which ultimately allows the terminal device to characterise thecell to an extent that it is able to decode PDCCH. However, to fullycharacterise the cell, the terminal device should also decode the systeminformation carried in the System Information Block(s) (SIB(s)). Inaccordance with this example embodiment, it is assumed that one aspectof the cell characterisation carried in SIB is a definition of therestricted frequency bandwidth that is to be used by the base station.For example, a SIB may be modified to carry an indication of upper andlower frequencies for the restricted frequency band, or a centralfrequency and bandwidth. However, in order for the terminal device toestablish the restricted frequency band to be used by the base station,the terminal device must read SIB in this example.

In a conventional LTE-based system, SIB is transmitted within the PDSCHregion of each subframe on the subcarriers identified using PDCCH. Thusa conventional terminal device can simply buffer and process an entiresubframe to first determine from PDCCH on which subcarriers SIB islocated, and decode SIB accordingly. However, to allow areduced-capacity terminal device that is unable to buffer and process anentire subframe to derive SIB, a pointer to the location of SIB may beprovided in accordance with embodiments of the invention. There areseveral possible techniques for indicating the location of SIB.

For example, the PBCH may be modified to indicate a frequency rangewithin which the SIB exists. PBCH contains spare bits that are notcurrently used and could be used to indicate the frequency range withinwhich SIB exists. A reduced-capacity terminal device may thus determinethe frequency range in which SIB is transmitted, and then buffer andprocess an appropriate part of the PDSCH region to read SIB.

Another approach would be to define a specially formatted signal withinthe control region (i.e. the region that contains PCFICH, PHICH andPDCCH as described above) to indicate a frequency range in which SIBresides. In accordance with established techniques, the CRC of a PDCCHsignal is XOR-ed with a radio network temporary identifier (RNTI) so thePDCCH signal is only decoded (de-masked) by the terminal device, orgroup of terminal devices, to which the PDCCH is directed (i.e., aterminal device associated with the RNTI). Accordingly, the speciallyformatted signal within the control region could, for example, be aPDCCH signal whose CRC is XOR-ed with an RNTI associated withreduced-capacity terminal devices, e.g. in this example MTC devices.Such an RNTI may, for example, be referred to as an MTC-RNTI. Thisspecial PDCCH signal could, for example, indicate a “downlink resourceallocation 0” message normally used to indicate which resource blocks(equivalent to frequencies) that are allocated to a terminal deviceassociated with the relevant RNTI. However, in accordance with anembodiment of the invention, a reduced-capacity terminal device may beadapted to interpret this information as an indication of a frequencyrange f1 to f2 within which the SIB could exist. The terminal devicecould then seek to decode SIB in that frequency range. A special formatPDCCH such as this might only be provided in some sub frames and notothers. For example, this “SIB-locating” PDCCH signal could exist in thefirst subframe (subframe 0) of every frame for which the system framenumber (SFN) mod 64=0. It will be appreciated that resource allocationsother than “downlink resource allocation 0” could alternatively be usedto convey the SIB frequency information. FIG. 8 is a flow diagramschematically representing this approach.

Thus, in step Si of FIG. 8, a reduced-capacity terminal device seeks todecode PDCCH using an RNTI associated with the reduced-capacity terminaldevice (MTC-RNTI). Processing then proceeds to step S2.

In step S2 the reduced-capacity terminal device determines whether ornot the PDCCH is one of a special format for “SIB-locating” (i.e.whether or not it can be decoded using the MTC-RNTI to derive a“downlink resource allocation 0” message). If the terminal devicedetermines the PDCCH is not “SIB-locating”, processing follows thebranch marked “N” back to step S1 where the terminal device seeks todecode a subsequent PDCCH. However, if the terminal device determinesthe PDCCH is “SIB-locating”, processing follows the branch marked “Y” tostep S3.

In step S3 the terminal device derives an indication of the frequencywithin which SIB is to be found from the decoded “SIB-locating” PDCCHmessage. Thus the terminal device determines from this message thefrequency range in which SIB may be present in future subframes.Processing then proceeds to step S4.

In step S4 the terminal device buffers the control region and a regionof PDSCH corresponding to the frequency range f1 to f2 determined instep S3. The terminal device then proceeds to decode PDCCH usingconventional techniques for determining the subcarriers on which SIB iscarried (i.e. using SI-RNTI) and acquires SIB from the buffered PDSCHregion. Thus the terminal device “knows” from step S3 that thesubcarriers carrying SIB will be somewhere in the frequency range f1 tof2, and in step S4 the terminal device determines the actual set ofsubcarriers within the range of frequencies f1 to f2 which is used tocarry SIB in the subframe. Processing then proceeds to step S5.

In step S5 the reduced-capacity terminal device determines whether ornot SIB has been successfully acquired in step S4. If SIB is notacquired processing follows the branch marked “N” back to step S4 wherethe terminal device seeks to decode a subsequent PDCCH. However, if theterminal device determines SIB had been acquired, processing follows thebranch marked “Y” to step S6.

In step S6 the terminal device derives restricted frequency bandinformation (for example upper and lower frequencies f1* and f2*) fromSIB. The exact manner in which the restricted frequency band informationis carried by SIB will depend on the implementation at hand. Processingthen proceeds to step S7 where the radio resource control connectionprocess may proceed. The restricted frequency band information definedby the upper and lower frequencies f1* and f2* communicated by SIB inthis way may be used to define the restricted frequency band forsubsequent higher-layer data communication as described above, or may beused simply to define a restricted frequency band for subsequent RRCconnection signalling, with a replacement restricted frequency band forhigher-layer data communication being defined by the subsequent RRCconnection signalling.

Another mechanism for ensuring a reduced-capacity terminal deviceaccording to an embodiment of the invention can acquire SIB is for thelocation of SIB to be specified in an amended 3GPP specification(standard). For example, the relevant specifications could be amended toindicate a location of the first block of the SIB (SIB 1). The locationsof subsequent blocks of SIB (SIB2, SIB3, SIB4 . . . , etc.) need not bestandardised, because the locations for these SIBs can be provided in aprevious SIB. For example, the first SIB block (in a standardisedlocation) could indicate to terminal devices where future SIB blocksreside. For example SIB1 could be in a known location in the frequencyspace and the frequency range f1 to f2 in which SIB2 to SIB11 residecould be signalled in SIB1.

Another mechanism for ensuring a reduced-capacity terminal deviceaccording to an embodiment of the invention can acquire SIB is byconstraining SIB (e.g. in standard specifications) to always occur atthe same location from frame-to-frame, but without specifying anyparticular location. If, for example, the SIB is repeated every 64frames, a terminal device could derive the location of the SIB using thePDCCH in frame 0. The terminal device would not be able to decode theSIB in frame 0 because the terminal device would not have known inadvance within which frequencies f1 and f2 the SIB resides, and so wouldnot have been able to buffer the necessary frequency range (unless bycoincidence). However, based on the SIB location derived from PDCCH insub frame 0, and assuming SIB is constrained to be located in the samefrequency range in frame 64, the terminal device could buffer theappropriate frequencies in frame 64 to acquire SIB.

Once SIB has been acquired by the reduced capacity terminal device usingany of the above described techniques, the terminal device is able toderive the restricted frequency band that will be used by the basestation for further communications since this can readily becommunicated by SIB according to any pre-arranged technique. Thus theterminal device is aware of what frequency ranges will be used for RRCconnection signalling for reduced capacity terminal devices. Forexample, the range may be defined as spanning frequencies f1* to f2*.

The terminal device may then proceed to connect to the network supportedby the base station using the PRACH (physical random access channel).The terminal device can be configured to listen for a “random accessresponse” only within the frequency range f1* to f2*, and the basestation (eNode B) can correspondingly be configured to send randomaccess response messages to reduced-capacity terminal devices only inthis frequency range.

The reduced capacity terminal device may then complete its RRCconnection process in a broadly conventional manner, except for onlylistening (i.e. buffering data) for responses from the network in thef1* to f2* frequency range, the base station being configured to onlyrespond in this range. In accordance with conventional RRC connectionprocedures the terminal device will receive a “radio bearer setup”message. This message may be adapted to indicate a new frequency range,f1# to f2#, to be used by the base station as the restricted frequencyband on which higher-layer data is to be communicated. The restrictedfrequency band f1# to f2# might be terminal-device specific or could beapplicable to a plurality of terminal devices (e.g. a group of UEs)depending on the implementation at hand.

At this stage the reduced-capacity terminal device is aware of therestricted frequency band that the base station will be using tocommunicate higher-layer data to the terminal device. Accordingly, theterminal device can proceed with buffering PDCCH and the restrictedfrequency band of PDSCH, and the base station can proceed with onlyallocating the terminal device with downlink resources on PDSCH withinthe restricted frequency band, so that higher-layer data may becommunicated from the base station to the terminal device in the mannerdescribed above, for example with reference to FIG. 7.

While a connection is ongoing, the frequency range f1# to f2# could bemodified for a given terminal device (i.e. the range of frequencies thatthe terminal device should buffer for decoding could be changed duringthe lifetime of the connection). A change in the restricted frequencyband f1# to f2# could be signalled using RRC signalling or MACsignalling. For example, replacement values for f1# and 12# could beencoded in a MAC header of PDUs transmitted to a terminal device duringan ongoing connection.

In order for a reduced-capacity terminal device to remain pageable whenin RRC idle mode, the terminal device may configure itself to buffer anappropriate part of the downlink frames having regard to where pagingmessages are transmitted. The base station may have previously signalledthe appropriate portion of the downlink subframes where paging messagesmay be located. The terminal device may have been signalled thisinformation, for example, by system information or other RRC signalling.What is more, in some examples, a paging message may be modified toinclude an indication of the restricted frequency band to be used forsubsequent paging messages/communications.

It will be appreciated that various modifications can be made to theembodiments described above without departing from the scope of thepresent invention as defined in the appended claims.

For example, in the specific examples described above informationidentifying the restricted frequency band is defined by standardisation,or communicated from the base station to the reduced capacity terminaldevice. However, in principle a reduced capacity terminal device may beconfigured to determine the restricted frequency band it wishes to use,and communicate this to the base station. For example, an indication ofa terminal device's chosen restricted frequency band may be conveyed ina random access channel access (RACH) by selection of an appropriatepreamble in accordance with a predefined scheme for mapping selectedpreambles to restricted frequency bands. However, in general it will bemost appropriate for the base station to determine the restrictedfrequency band since the base station can more easily take account ofother terminal devices operating in the cell and select an appropriaterestricted frequency band for a given terminal device accordingly.

Furthermore, while the above embodiments have primarily focused ondefining a restricted frequency band in which resource allocations forreduced-capacity terminal devices are provided such that the terminaldevices need not buffer the entire subframe, the same principle couldalso be applied in the time domain. That is to say, some embodiments ofthe invention may be based on pre-establishing a restricted number ofsymbols (timeslots) within which higher-layer data, e.g. on PDSCH inLTE, may be communicated from a base station to a reduced-capacityterminal device, wherein the restricted number of symbols is fewer thanthe number of symbols allocated for higher-layer data for conventional(“full-capacity”) terminal devices. Thus a base station may beconfigured to only allocate downlink resources for a terminal device onPDSCH within a restricted number of PDSCH symbols. Because the terminaldevice knows in advance that it will only be allocated PDSCH resourceswithin the restricted number of symbols, the terminal device does notneed to buffer and process any PDSCH resources from other symbols. Thisprinciple is shown in FIG. 9.

FIG. 9 schematically represents two arbitrary downlink subframes(identified as subframe n and subframe n+1) as seen by areduced-capacity terminal device according to an embodiment of theinvention. FIG. 9 is in some respects similar to FIGS. 6 and 7, andaspects of FIG. 9 which correspond to aspects of FIGS. 6 and 7 are notdescribed again in detail.

In this example it is assumed a base station and a reduced-capacityterminal device have both established that higher-layer data is to becommunicated from the base station to the terminal device only within arestricted number of OFDM symbols (X) in each subframe. In this examplethe restricted number of symbols immediately follow the control region,but that need not necessarily be the case. For the sake of a concreteexample, the restricted number of symbols is assumed here to be 4.Information on the restricted number of symbols can beestablished/shared between the base station and terminal device usingthe same principles as described above for establishing/sharing therestricted frequency band information.

FIG. 9 represents in shading the areas of each subframe which thereduced-capacity terminal device is arranged to buffer ready forprocessing. The buffered part of each subframe comprises a controlregion 600 supporting conventional physical-layer control information,such as the PCFICH, PHICH and PDCCH channels as discussed above and arestricted PDSCH region 902. The physical-layer control regions 600 thatare buffered by the reduced-capacity terminal device are the same as thephysical-layer control regions 600 buffered by the smart phone device506 as represented in FIG. 6. However, the PDSCH regions 902 carryinghigher-layer data which are buffered by the reduced-capacity terminaldevice are smaller than the PDSCH regions 602 buffered by the smartphone device 506 as represented in FIG. 6. This is possible because, asnoted above, in accordance with embodiments of the invention, a basestation may be adapted so that higher-layer data on PDSCH is allocatedto reduced-capacity terminal devices only on symbols within thepre-established restricted number of symbols X. Because the terminaldevice “knows” this, the terminal device can be configured to ignore(i.e. not buffer) PDSCH resources that are outside the restricted numberof symbols X.

Also schematically shown in FIG. 9 by black shading are example PDSCHdownlink allocations 904 for the reduced-capacity terminal device. Thereduced-capacity terminal device may be configured to derive itsspecific PDSCH downlink allocations for each subframe from PDCCHtransmitted in the control region 600 of the subframe in accordance withthe defined standards. That is to say, the principles for communicatingto the reduced-capacity terminal device the downlink allocations 904 ithas been allocated does not need modifying to implement an embodiment ofthe invention (the terminal device simply operates on the understandingthat higher-layer data will only be transmitted on the allocatedsubcarriers for the restricted number of symbols).

Thus, a reduced-capacity terminal device may buffer for each subframethe entire control region 600 (shaded dark grey in FIG. 9) and therestricted PDSCH region 902 (shaded light grey and black in FIG. 9) andextract the higher-layer data allocated to the reduced-capacity terminaldevice (shaded black in FIG. 9) from the restricted PDSCH regions 902based on allocation information conveyed in the control region 600.

In one example LTE-based implementation of an embodiment of theinvention, each subframe is taken to comprise 14 symbols (timeslots)with PDCCH transmitted on the first three symbols and PDSCH istransmitted on the remaining 11 symbols. Furthermore, the wirelesstelecommunications system is taken in this example to operate over asystem frequency band of 20 MHz (100 resource blocks) with apre-established restricted number of symbols of 4 used for communicatingwith reduced-capacity terminal devices operating in accordance with anembodiment of the invention.

In this case, and as already discussed above, a conventional terminaldevice, such as the smart phone 506 shown in FIG. 5, is required tobuffer a region of 100 resource blocks (20 MHz) by 14 symbols, which is1400 elements. However, a reduced-capacity terminal device according tothis embodiment of the invention might only buffer the control region,which is 100 resource blocks (20 MHz) by 3 symbols, and the restrictedPDSCH region, which is 100 resource blocks (20 MHz) by 4 symbols.Accordingly, a terminal device operating in accordance with this exampleembodiment of the invention need only buffer a total of(100×3)+(100×4)=700 elements. This is significantly less than (by arounda factor of two) the 1400 elements buffered by a conventional device. Aswith the restricted frequency band embodiments described above this hasadvantageous consequences in terms of reduced memory and processingcapacity requirements for the terminal device receiving higher-layerdata only on the restricted number of symbols.

In general, it is expected the restricted frequency-based embodimentsmay be preferred in some implementations because they do not “waste”resources. This is because all of the PDSCH resources outside therestricted frequency band can be allocated for use by conventionalterminal devices. However, in an example embodiment using a restrictednumber of symbols, it is less easy for the transmission resourcesoutside the restricted number of symbols on subcarriers allocated toreduced-capacity terminal devices to be re-used by conventional terminaldevices (although they could be allocated to other reduced-capacityterminal devices adapted to buffer only a subset of the availablesymbols supporting PDSCH). Furthermore, a restricted frequency-basedapproach may simplify other aspects of the implementation. For example,a conventional SIB extends across all available symbols and so anapproach in which a reduced capacity device is able to only buffer areduced number of symbols may rely on further modifications, forexample, a dedicated SIB spanning a reduced number of symbols may bedefined to convey the relevant information to reduced capacity devices.

It will be appreciated that other embodiments of the invention maycombine aspects of a restricted frequency band and a restricted numberof symbols.

What is more, although embodiments of the invention have been describedwith reference to an LTE mobile radio network, it will be appreciatedthat the present invention can be applied to other forms of network suchas GSM, 3G/UMTS, CDMA2000, etc.

Thus, a method for communicating data between a base station and aterminal device in a wireless telecommunications system has beendescribed, for example an LTE-based system. The wireless communicationsystem uses a plurality of frequency sub-carriers spanning a systemfrequency band. Physical-layer control information for the terminaldevice is transmitted from the base station using sub-carriers selectedfrom across the system frequency band, for example to provide frequencydiversity. However, higher-layer data for the terminal device istransmitted using only sub-carriers selected from within a restrictedfrequency band which is smaller than and within the system frequencyband. The terminal device is aware of the restricted frequency band, andas such need only buffer and process data within this restrictedfrequency band during periods where higher-layer data is beingtransmitted. The terminal device buffers and processes the full systemfrequency band during periods when physical-layer control information isbeing transmitted. Thus, a terminal device may be incorporated in anetwork in which physical-layer control information is transmitted overa wide frequency range, but only needs to have sufficient memory andprocessing capacity to process a smaller range of frequencies for thehigher-layer data.

Further particular and preferred aspects of the present invention areset out in the accompanying independent and dependent claims. It will beappreciated that features of the dependent claims may be combined withfeatures of the independent claims in combinations other than thoseexplicitly set out in the claims.

REFERENCES

-   [1] ETSI TS 122 368 V10.530 (July 2011)/3GPP TS 22.368 version    10.5.0 Release 10)-   [2] UK patent application GB 1101970.0-   [3] UK patent application GB 1101981.7-   [4] UK patent application GB 1101966.8-   [5] UK patent application GB 1101983.3-   [6] UK patent application GB 1101853.8-   [7] UK patent application GB 1101982.5-   [8] UK patent application GB 1101980.9-   [9] UK patent application GB 1101972.6-   [10] R1-113113, Pantech USA, 3GPP TSG-RAN WG1 #66bis meeting,    Zhuhai, China, 10 Oct. 2011 to 14 Oct. 2011-   [11] Holma H. and Toskala A, “LTE for UMTS OFDMA and SC-FDMA based    radio access”, John Wiley and Sons, 2009

1. A method of operating a mobile device for receiving data in awireless telecommunications system using radio subframes comprising aplurality of symbols, the method comprising: receiving and bufferingphysical-layer control information transmitted by the base station usinga first group of the symbols in a radio subframe; receiving andbuffering higher-layer data transmitted by the base station using asecond group of the symbols of the radio subframe, wherein the number ofthe symbols in the second group is less than the number of the symbolsof the subframe available for transmitting higher-layer data to otherterminal devices; processing the buffered physical-layer controlinformation to determine an allocation of higher-layer data for theterminal device within the second group of the symbols in the subframe;and processing the buffered higher-layer data to extract the allocatedhigher-layer data for the terminal device from the second group of thesymbols in the subframe.
 2. A mobile terminal for communicating datawith a base station in a wireless telecommunications system using radiosubframes comprising a plurality of symbols, wherein the mobile terminalis configured to: receive and buffer physical-layer control informationtransmitted by the base station using a first group of the symbols in aradio subframe; receive and buffer higher-layer data transmitted by thebase station using a second group of the symbols of the radio subframe,wherein the number of the symbols in the second group is less than thenumber of the symbols of the subframe available for transmittinghigher-layer data to other terminal devices; process the bufferedphysical-layer control information to determine an allocation ofhigher-layer data for the terminal device within the second group of thesymbols in the subframe; and process the buffered higher-layer data toextract the allocated higher-layer data for the terminal device from thesecond group of the symbols in the subframe.
 3. A method of operating amobile device for receiving data in a wireless telecommunications systemusing radio subframes comprising a plurality of symbols, the methodcomprising: receiving physical-layer control information transmitted bythe base station using a first group of the symbols in a radio subframe;receiving higher-layer data transmitted by the base station using asecond group of the symbols of the radio subframe, wherein the number ofthe symbols in the second group is less than the number of the symbolsof the subframe available for transmitting higher-layer data to otherterminal devices; processing the physical-layer control information todetermine an allocation of higher-layer data for the terminal devicewithin the second group of the symbols in the subframe; and processingthe higher-layer data to extract the allocated higher-layer data for theterminal device from the second group of the symbols in the subframe. 4.A mobile terminal for communicating data with a base station in awireless telecommunications system using radio subframes comprising aplurality of symbols, wherein the mobile terminal is configured to:receive physical-layer control information transmitted by the basestation using a first group of the symbols in a radio subframe; receivehigher-layer data transmitted by the base station using a second groupof the symbols of the radio subframe, wherein the number of the symbolsin the second group is less than the number of the symbols of thesubframe available for transmitting higher-layer data to other terminaldevices; process the physical-layer control information to determine anallocation of higher-layer data for the terminal device within thesecond group of the symbols in the subframe; and process thehigher-layer data to extract the allocated higher-layer data for theterminal device from the second group of the symbols in the subframe.